Differential control circuit



Feb. 13, 1951 B. M. oLlvl-:R

DIFFERENTIAL CONTROL CIRCUIT 4 Sheets-Sheet l Original Filed Feb. 24, 1944 /NVE/VTOR BM. OL /VER BY ATTORNEY A T TORNE V 4 Sheets--Shee'I 2 B. M. OLIVER DIFFERENTIAL CONTROL CIRCUIT Feb. 13, 1951 original Filed Feb. 24, 1944 Feb. 13, 1951 B. M. OLIVER DIFFERENTIAL CONTROL CIRCUIT original Filed Feb. 24, 1944 4 Sheets-Sheet 5 Patented Feb. 13, 1951 2,541,276 DIFFERENTIAL CONTROL CIRCUIT Bernard M. Oliver, New York, N. Y., assignor to Bell Telephone Laboratories, incorporated, New York, N. Y., a corporation of New York @riginal application February 24, 1944, Serial No. v 523,721. Divided and this application May 28,

1945, Serial No. 596,239

1 Claim.

This invention relates to control circuits and `more specifically to arrangements ofrthis character responsive to two input signal potentials. This application is a division of application, Serial No. 523,721, filed February 24, 1944.

1t is an object of this invention to provide a simple and eiiicient control circuit for controlling the operation of a relay or other device by two direct voltages, the ratio of the amplitudes of which varies.

It is another object of this invention to provide a novel relay control circuit responsive to two Y input signal potentials and employing a single two-terminal relay coil in the output thereof, the arrangement being such that certain undesired signal components are suppressed and thus do not cause unwanted operation of the relay.

An illustrative embodiment of the invention and one of its applications will be described below in connection with an automatic tracking radar system wherein it is desired to switch from automatic to manual tracking upon the failure or fading of normally received incoming echo pulses or when for any reason the incoming echo pulses arrive at such advanced or retarded times that the automatic handling of them for automatic tracking would fail or become ineiiicient, but it will be obvious that the control circuit of this invention has much broader application than -to radar systems.

The heart of the control circuit forming part of the illustrative embodiment comprises two tubes connected so that they have a common cathode resistor and the control elements of the two tubes have applied thereto, respectively, two direct voltages, the ratio`of the amplitudes of which varies, the output circuit of one only of the tubes containing a relay coil or other means for utilizing the output current. When the'signal voltage of the tube having the relay coil in its output circuit increases with respect to the other vsignal voltage by a predetermined amount, the load current through the relay increases to an extent sufcient to operate the relay, but if this first-mentioned signal voltage decreases with respect to the other signal voltage, the relay remains deenergized because not suicient load current passes through its coil to retain it in the operating position. In the specific application of the invention herein described, the two direct l potentials are integrated positive halves of alternating potential `waves to either or both of which the echo pulses may be added dependent upon the time of their reception with respect to the occurrence of the half waves An advantage box il to the receiver I3.

of this circuit is that, as will be described more fully below, the noise or other spurious signal components in the incoming current paths do not cause the relay to operate at times it should not. The relay may be used in circuits to give a visible or audible indication of the tracking condition or produce a switching operation.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which:

Fig. 1 is a schematic block diagram of a radar system employing a relay control arrangement in accordance with the invention;

Fig. 2 is a circuit diagram of a portion of the automatic range tracking unit forming part of the system of Fig. 1; Y

Fig. 3 is a circuit diagram, partly schematic. of the automatic tracking indicator and control circuit forming part of the system of Fig. 1 and including the relay control, double triode tube Vl and its associated connections in accordance with the invention; and

Figs. 4 and 5 are diagrammatical and graphical representations to aid in understanding the invention.

Referring more particularly to the drawings, Fig. 1 is a single line block diagram to show the relationship of the various elements of a radar system utilizing a control circuit in accordance with the invention. In the arrangement of Fig. 1, an ultra-high frequency pulse modulated wave is produced in the transmitter Hl. The transmitter Ymay comprise, for example, a high voltage rectifier of any suitable form which supplies about 12,000 volts direct current to a suitable charging circuit or element capable of producing a still higher voltage. After the charging voltage builds up to about 21,000 volts, any suitable rotary spark gap discharges the capacitor in the charging circuit. This discharge takes place in about 1 microsecond and causes a magnetron oscillator in the transmitter to oscillate for this brief period and send short pulses of radio frequency energy through a T-R box l l to an antenna l2 which, for example, includes a wave guide and a parabolic reiiector. A suitable antenna is disclosed in an application by A. P. King, Serial No. 499,450 led August 21, 1943, and in a corresponding British Patent 586,689, complete accepted March 2'7, 194'?. Radiations from the antenna g strike one or more objects and produce reflections or echoes therefrom which are received by the antenna I2 and transmitted through the T-R The T-R box can be vannate of any desirable type, for example, that employing a Western Electric Company 709-A tube in a resonant cavity. This tube is filled with an ionizable gas and has a small gap therein. During reception of the low voltages of the received energy, the gas is not ionized, the cavityis tuned to resonance and the received energy is applied to the receiver I3. During the emission of a transmitted pulse from the transmitter l0, the voltage due to the pulse ionizes the gas thus detuning the cavity and substantially preventing'the'energy of the pulse from reaching the receiver "|3.

In the receiver I3 the received waves fare heterodyned to a convenient intermediatefrequency and these intermediate frequency waves are am-1 plied, detected, and applied to thesignallselector 20 in the automatic range tracking unit I4. The unit I4 will be described more fully below.

Pulse energy from the transmitter |`,'which is in the nature of a synchronizing pulse, controls 4 the range unit I5 whichv is'essentiallyayariable "jdelay'circuit or unit whichproduces af-'pulsellll of predetermined lengthv acontrollable'period'of "time :after the initiation of the pulsefrom the transmitter Iii (which is-in the same'p'osition'as.' or'slightly before or slightly aiterythe pulse |00 in Fig. 4-A). jin an application of L. A. MeachamjSerial No. 491,791, led June 22,1943, and which is'now U. S. Patent No. 2,422,204. The output pulse from the A suitable range unitv is disclosed circuit I is applied to-a delay circuit'andpulse generator 2| which, for exampla'produces a pulse |08 (see Fig. 446i) which has a duration Vcorresponding `to a range of, for example, 40() yards, the pulse |08 being initiated after a time interval corresponding to a range o f 400 yards from the ,start of the plllS@ trom the'- range uni'tIE." Asuitable circuit to perform the functions of the unit 2| isdisclosed in a copending application of'B. M. Oliver, Serial No'. 523,722, led February 24,1944,VJ j and which is now U. S. Patent No.v 2,451Q632.A The output pulse |08 from the delay circuit and pulse generator 2| (see Fig.V 440) is also 'fed tothe signalselector 20. A` suitable signal selector is lalso shown in the above-'mentionedOliver-applie cation. The output pulse II from the range unit I5 lis also applied to a pulse generator 22 which produces a negative or notch pulse |02 (shownin Fig. 4-C) which is applied to the gating' waves f generator 23. The pulse |02 has atime duration corresponding to l2l0 yards range, Vfor example,

' "and this pulse is started by the range'unit pulse |0I.v Fig. 4-D shows two gating waves |03 and |04 which are produced by the'generatorv 23. The waves |03 and |34 are appliedl to a range detector 25 to which is also applied the'selectedportion of the video signal from the Vsignalselector 20. This selected signal is representedby'the pulse |02 in Fig. 4H and is produced' by applying a wave such as that shown in Fig. 4-F (representing received and detected pulse |00 corresponding to the transmitted pulse, various echoes |01 and noise voltage components) to the Vsignal selector along with the 40G-yard positive or pedestal pulse |08. The pulse Hi8 causes'the signal selector 20 to pass current for the duration of this pulse and reject all portions of the signal produced by the receiver i3 which do not occurwithin the time span of the 400-yard pulse 08. This is represented in Fig. 4-H, the selected echo signal being shown by the pulse I09. In other words,

the signal selector 20 has an outputcurrent only during the time span of the pulsev |08and the position of this pulse with respect" to the-pulse --spectively the gating waves'I-Il 'and |04 from the "amplifier'i24" and to the plates/"ofl both of which'.

is applied the selected video signal from the cir-- -cuit 20. Integrating condensers are connected toV the cathodesof the diodes and voltages are pro-- duced thereacross which are respectively reprefffsentative ofthe-total current passed by the di ""odes during thepositive halves of the waves |03.J

" `a`ndf|04by means which will be described below.v

I f t he pulse |09 vis not symmetrically postioned.

lf inrtime witlresipc't to the gating waves |03 and.

|04 (it Ahas been shown as being symmetrically positioned with respect to the middle positive puls'esof the waves |03 and |04) a differential current is produced which is utilized to drive a 'finotor "28" to"control #the 'range unit v*I 5fv in' fsuch a. way as `f to =vary the" position 'of 1 the -frange unit i' pulsefll'IIshown` in'Fig. 4-B witlrrespectto they pulse' |00 shown in Fig. 4--A.Y The current used toA drive the motor '28fis'produced inthe'modulator 26 to which the sig-nar'tzurrenty fromf-the range Vdetector"-25 is `applied'inffadditiortto 1G0-cycle:

f waves from' the source35'acting through a--phaser shifter 29.' The output of the modulator 26 which is a GO-cycle wave amplitude-modulatedThy-the signals fromthe circuit? 25 is amplied-inthe am plier'Zl 'and' applied to the motor-'28"through-an amplii'lerf30, contactSI", and armaturerSS-ofcthe control relay` 34 which' latter is operated ybyrn'ieans "of the automatic tracking indicator'- and vcontrol Y circuit I-tofbe'described more fully below.

Before describing `in detail the circuit Y I6, a

' 'more 'detailed' description of the automatic range tracking unit I4L with reference to' Fig*l 2rv will VAbe given. Fig.' 2 show's'tne pulse generator T22,

f'f'th'e 410-kilocy'cle"generatorf23 of the two gating waves; amplia-erfzatrange-uetsctor2s and direct coupled amplifier 15A. The` pulse 'generatorr 22 crimpr'ises a tube VIto' the control-'grid of which f i's'applied-through a resistor 40 the-positive'fpulses 10| (one foreach transmittedpulse` |00) from the*range :unit 5. Y 'The cathode" cil this tube is connected 'to' lthe suppressor grid and4 also to *ground through lthe `parallel connected condenser 4| and resistor 42. The cathode'isalso connected vtl-ir'o'ughv resistors' 143 andi" 44 tofthe'positive Yterininal' of afsourceli' of vconstant''potential of I `f300` v'oltS, 'for example. While' thel source-45 fhas been" rep'resented 'schematically `as a' battery; the

nectedfbetweenfthe co'i'nm'onterminall of ftliecon- The-camere 'ning 'fpoteameters when r th ranger una puise Y in if is applied rter miseria74 or; ureltube fvl.

this tube conducts plate current for the instant.

that the control grid is above the cut-01T voltage. The pulse of plate current drawn .by VI during the time of the range unit pulse charges the condenser through the path comprising this condenser, the condenser 48, theplate-cathode resistance of Vl, and the condenser 4|. This causes the plate voltage to drop about 200 volts and since condenser 48 is much larger than condenser 5|, the grid of the tube V2 is driven negative by the same amount. The LC network comprising the members 50 and 5| begins an oscillation'which is quenched after one-quarter cycle because the voltage across it begins to swing positive and the grid of tube V2 begins to draw current. The voltage applied to the grid of the tube V2 has the wave form shown in Fig. 4-C. The period of this oscillation can be adjusted by, means of the condenser 5| which is adjusted to make the duration of the pulse |02 in Fig. 4C equal to a period of time equivalent to a 1200- yard range, for example. The large negative grid voltage pulse |02 cuts off the tube V2 for a length of time equal to substantially one-fourth of the period of one oscillation of the network T and produces, by means of apparatus now to be described, plate voltage waves |03 and |04 shown in Fig. i-D. l

Tubes V2 and V3 collectively comprise a. generator of the gating waves |03 and |04 which are 180 degrees displaced from each other andare as shown in Fig. -D. These waves are sine waves of a frequency of about L110 kilocycles, this frequency being that required to produce three complete cycles within a period of time corresponding to a range of 1200 yards. Associated with tube V2 is the network 52 comprising a transformer 53 having a primary winding 54 and a secondary winding 55. The primary winding 54 is shunted by a condenser 56 and the mid-point of the winding 54 is connected to the cathode of the tube V3, the mid-,point of the winding 55 being connected to ground. The winding 54 has one of its terminals connected to the plate ofthe tube V2 and through a condenser 51 and resistor 58 tothe control grid ofthe tube V3. The winding 54 has its other terminal connected through the resistor 59 to the positive terminal of thedirect current source 45 and through a condenser 60 to ground. The terminals of the secondary winding 55 of the transformer 53 are connected to any suitable push-pull amplifier 24. The cathode of the tube V2 is connected to ground and the cathode of the tube V3 is connected through .the resistor4 6| to ground. A grid leak resistor 62 is connected in the grid-cathode circuit of the tube V3 while the plate of the tube V3 is connectedthroughthe resistor 63 to the upper terminal of the winding 54.

'I'he grid of the tube V2 receives the 1200-yard negative pulse |02 from the tube VI. Plate current for the tube V2 normally ows through the transformer winding 54 in the network 52. The voltage pulse |02 applied to the grid of the tube V2 cuts'the tube off and the change in plate current of V2 causes the tuned circuit of the net work 52 to oscillate. When the grid voltage of the tube V2 rises above cut-off (after a period of time corresponding to a range of 1200 yards), plate current flows again through V2, and the low plate resistance of this tube damps out the oscillations.

The tube V3 is used to supply feedback to the network 52 of just the proper amount to make upfor its losses and thereby maintainaconstant Vamplitude for all cycles in the oscillation. `The condenser 5| is adjusted until the duration of the large negative grid voltage wave'l02 extending below cut-off of the tube V2 is just long enough to produce three complete 4.oscillation cycles of the network 52 before the oscillations are damped out. The wave forms of these oscillatory waves |03 and |04 are shown in Fig. 4-D.

The voltage waves |03 and |54 produced at the respective terminals of the secondary transformer winding 55 are amplified by any suitable pushpull amplier 24 and applied respectively to the two plates of the double diode tube V4. Equal resistors 64 and 55 are connected in series across the output terminals of the push-pull amplifier 24 and the common terminal of these two resistors is connected through a resistor 55 to ground. The left cathode of the tube V4 is connected through the parallel connected resistor 67 and condenser 68 and the resistor 55 to ground, while the right cathode of the tube V4 is connected through the parallel connected resistor 'i0 and condenser and the resistor 555 to ground. The two cathodes are also connected through the series resistors 12 and "i3, respectively, to the input terminals of the direct coupled ampliiier 25A which is of any suitable form. Equal condensers 74 and 75 are connected across the input terminals of the amplifier 25A, the common terminal of the two condensers being connected to ground. The elements l2 and 'I4 and i3 and 'i5 serve as two low-pass filters.

The action of the range detector is as follows: The amplified output waves of the 4l0-kilocycle generator 23 (such as those shown in Fig. 4-B) are applied to the two plates of the double diode V4. An adjustment can be made in the push-pull amplifier 24. so that the voltages applied to the two plates of the tube Ve are equal when no video signal from the signal selector 20 is applied to the plates oi the tube V4. The signal from the signal selector is applied to the common terminal of the resistors 54 and @5 and this is applied equally to the two plates oi the double diode tube V4. A coupling condenser 'i0 can be used in this input circuit if desired. The period of the selected signal shown in Fig. #i-H is, as pointed out above and as shown in Fig. e, of the proper length of time to correspond to 400 yards range and this 40G-yard pulse coincides with the time of the middle cycle of the two ilo-kilocycle sine wave oscillations. Once this adjustment is made, the relation between the ao-yard pulse shown in Fig. 4-G with respect to the Waves shown in Fig. -D remains fixed even though the time of occurrence of all of these may vary with respect to the time of occurrence of the corresponding transmitted pulse |00, this variation being caused by the changes in time oi' occurrence of the range unit pulse iol when the apparatus is being utilized to track the selected target.

If no video signal is applied to the plates or the tube V4 from the signal selector 25, the current through the two halves or the double diode V4 will be equal and will appear as two series oi positive half sine waves E05 and H36, Fig, 4 5-1, as each half of the tube V4 conducts alternately. The pulses are integrated by the condensers 38 and ll. The resulting signal voltages are applied to the two grids of a balanced direct current amplifier arrangement represented schematically by the box 25A in Fig. 2 through the lters 12, 'H4 and '|3, 15 and in turn produce equal voltages.

If there is a video signal exactly in the center of the 40G-yard pulse shown in Fig. 4-G, its voltage will add equally to the voltage applied to the two sectonscf the tubelzwv to @cause rincreased currents. to now; The; currents ithroughrtheitwo halves of the-double diode-Vwill bai-nereasedfby .thessame amount.v so that .the :two currents will still'ibe' equal. `As lbefore., this will :result .in :equal signal. .voltages :at Athe input of .the modulator 26 i If 'the.,selectedecho .signal .1.695 occursin..I the rst 200 yards'of .ther 40G-yard:rangeepulsegtoneh ha'ltof tubeVli, say:,.i;`or example, the rightilialf, willibeaconducting.. .The positive voltage :of .the video signal. willadd to thevolta'ge 'on this plateto cause anA increase in the' 110WY of current .through thizdiode. ,Thel voltage appliedto the 'leftlrplate of the tube :VQ Jwill benegative atthi's'instanttand theaselectedcsignal cannot cause :current to flow in :th'is'zhalfA of the.tube....A half cycle later. the left plate twill: be Dosi-tive and 'cause currenttto floxvfbut thei- .Video :signal Will v.not be Lpresentito add'to this lcurrenty so thatvit will be.lessr.;than that which; flowed in .the right half.

If Ztheisignal from. the target 'occurs 'in the. second.200 yards of the. Lleyard. range. pulse!! 08, thercurrent-ilow through. the resistor `('liltvillLb'e increased'whilev the current iiow throughthef'resistor fili will remain normal.v The eect is .the Y reverse of :that which .takes placeunder thecon.- ditionsfidescribed in the .immediately 4preceding paragraph.` The .unequalvoltagestoiground at these resistors! are applied-to the inputcircuits of the balanced-direct coupledy ampli'er.-.25A`..and then applied-to the vmodulator 2%.

Thamodulatorzze preferably comprises ka bridge structure of four rectifier elements suchlas that shown n F. aA. yCowan Patent 2,025,158, :issued December 24,1935. An alternating currentffrom a suitablevsourcasuch as the sourceY of s60-cycle voltagel, is applied through .a 90'degreelphase shitting network2 to one diagonal of the bridge, thefother. diagonal being' connected to theoutput terminals of the. direct coupled ampIi'eruZEA. Thefmodulator 2&3.V operates in xaccordanc'e With the description inzthe Gowan patent to suppress they carrier fromthe source i 35 .and .transmit to th'e'output circuit of the modulator .substantially only. the upper and. lower sidebandsproducediby s theiamplitude modulation of this carrier byi'tlie signalinplut. The output wave iromath'e-.xnodue later, comprisingf a wcycle, Ysignalmodulated \vave,is ampliied'by the ampliiier 27 whichmay beiof :the conventional push-pull type and--bya second .amplifier 3@ of any suitable type,onefof the output terminals of this latter amplierbeingv connected to the contacts 3i Yofthe control 'relay 34. When the control relay 34, in a manner to be described more fully below, is operated -t'o .f

the automatic position, the amplier 3i) `is "con-l nected through the contact-'3l andi-.armature of the control relay 3t to a suitable .motori-:28 which is preferably oi the two-phase low inertia type. An uninodulated (S0-cycle voltagel is Tap"- plied to the second winding oi the motor 218 from the source S5. .Since the carrier inputwtorth modulator 25 is shifted 90 degrees byithe'pha'se shifter 29, the output of thev amplier-vSD will bear a plus or minus 90 degrees phase relation-"to the x;d phase excitation of the motor depending" on the direction'oi the unbalance which drives the modulator '28. Any imbalance voltage resulting from the received Asignal not occurring' symmetrically with respect to the two Vgating Wave'sfithat is, with'` respect to the vpulsesland |06 contained Within thespan't of ythe" 400'- yard pulse Hi8) therebyy `causes `rotation* of rthe 'armature of Vthe motor 28fwhich is mechanically -connectedf'to thevariable delaylor range-unit -i--S A 'to idrh'fevai variableuicondens'eraforming apartlof -saidiunitiin ionedirectioncor-Jtheotheie fThefro'- vtation is in.a directionttoevaryfthe timings'ofrthe output pulserofa;thef rangefunit fin; such'lfa Way 4r-thatathengatingwaives iarefrcentered about :the

th'e drixingivoltageato zerogwA dial (InOtfShOWn) withtrespectto theftransnijittedfpulse we is not necessarily ian; :accurate --measure 'fof theL range. Moreoverrit migntoccasionallysnappen' l.that :the selectingriemeyard. puise-1l 18 fishownv in VFig'.E Yii-Gr does-mot span .the clesirefd'iechoi'signal which cone dition mayiexist ininitialflylsettin'g the apparatus for :automatic `tracking 2operationf orl when the apparatus is .setuintotoperation again after-ra period when it has been turned off. I'-Insucha situation: lit is desirablev` t'o i be -f ableto i manually icontrolztheoperation l'of A theange unit 1, so A:that

the :range e 4dial :can give 1an I Aaccurate f indication of -the:=.range tcf-thei'vdesired target;- 'LA suitable simple manual system :has r :been-s schematically shownzin ligx'rl. In'this'4 ligure a yhandlwhe'elim servofory synch-rol system #comprising '1a sending 'Selsyn-'Si ,'ila. receiving rvSel'syn'dz fand Ian ampl-ier ltherconnecion irom-thefampli'er to theimotor 28 'fbeingl throng-h.' the manualcontact f32 fof vrthe Thefmotor-Z 23A-fis Vgeared or otherwise mechanically connected 'to the irota'i"y-arrnaturey of there'ceivingV S'e1syn182 .1' f'ngeneral, the v'voltage i induced -the receiving: Selsyn .by thel turning 'of Sthi'armature Tand"thesendinselsyn because of -the movement o'irthe handfwheel 18B is notisuicientft'o produce .a torquez-.largelenoughfto 'fdrive the frange :unit "so thei'ampiierl :S3 land motor v2:3 servela's a= torque amiolierf 'forfthei'receivingvselsyns A suitable 'servo systerhntnvolving-'a 'sendingfSeLay'n',`y a receiv- 'ingr .'Selsy'n,A` a power -ampliliier Iand: motor is dis# closedd an application-'of E. "1'. Burton, Serial No'. 491,789,'led:June 22,'1-1943i'andvfhich-'is now '-U. S. Patent l @162111434 ,255131 l In forderlfto op'erat'e itl-1e? control'l relay 3d frdm tharnanuaLft'o the automatic positionA 'andi vice vversaglrtheautomatic?trackingl indicator and conti'lfcircuitare fprov'id'ed.""f'l."li `circuit I6 is also' provided with an indicator to show when the :automatic tracking "apparatus is `ffollowing. the selectedftargetff- Ifli'e'oirciiit *IS comprises: 'a SO-de'greefphase shifter "Jil Afor#shiftingfthe ph'asef'of -th vgating 'wavesrroi'n the? generator l23,2 90- degrees, an -am `plfie'r 59| fior Jthesewaves,v anfautomatic tracking' indicaitorfanel l'control*detector 92 (calledl -the A. lT. 'L C. idetector) Similar to fthe; doubldio'de tubefV 'df Figz, anamplie93,*anautomatic tracking'dndicateraindconti'ot relayl94 (called-the A. T. 'I. C. relayiand adnautornatictracking- `indicator 95.Iv lhefer'ericev Willfnowbe l made' to Figi 3 for amore a detailed description -of thev apparatus comprising* the L4circuit I'G .i

Re'ferringncvir to 3, fgatin'g' waves Iy-03 fand secondary winding 55 of the transformer 53 are applied to the two control grids of the double triode tube V which with its associated circuits acts to shift the phase of these two waves by 90 degrees. The two control grids are connected to ground through resistors Il!) and respectively, and the twoV cathodes are connected to ground through resistors I I2 and i3 respectively. The two plates are connected to the positive terminal of the direct current source ti5 through resistor H4. Connected in parallel between the two cathodes of the tube V5 are two series connected circuits, one comprising the resistor |I5 and the condenser IIB and the other comprising the condenser I I'I and the resistor I8. The tube V5 serves as a double cathode follower tube to drive the phase shifter, and the outputs of this phase shifter are taken from the points C and D which are the respective common terminals of the two series connected circuits just described. (If desired the tube V5l can be connected between the members 23 and 2li in the automatic range tracking unit I4 to provide a cathode follower output for the generator 24. In such an arrangement the points A and B (the cathodes of the tube V5) are connected .to the member 24 and the points C and D connected to the member 9 I.)

The voltages applied to the tube V5 result in alternating voltages from points A and B to ground which are equal and 180 degrees out of phase with each other. Since this is true, the voltage between points A and B will be twice that of the voltage between either of these points to ground. These voltages are shown in the vector diagram of Fig. 5 by vectors AG and GB and the voltage AB is the sum of these two vectors. In this diagram the point A is used as a reference point and, therefore, the arrows for vectors AG and BG are not shown |80 degrees apart as would be the case if point G or ground were used as a point of reference. The currents I1 and'Iz flowing between points A and B by way of parallel paths ACB and ADB, will lead the voltage AB by 45 degrees as shown on the vector diagram, since each of these paths has a resistance (I i5 or I I8) in series with a capacitive reactance of the same magnitude at 410 kilccycles (3900 ohms). The

voltage drop Em across resistor IIS wi'l be in y phase with the current I1 as represented by vector AC. The voltage drop Ec1 across condenser I|`| lags behind current 11 by 90 degrees and is represented by the vector CB. The voltage drop Ec?l across the condenser I i3 lags behind current I2 by 90 degrees and is represented by the vector AD. The voltage drop Enz across the resistor ||5 is in phase with the current I2 and corresponds to vector DB.

The resulting voltage between C and D is 90 degrees ahead of the voltage AB. On the vector diagram of Fig. 5 the voltage from point C to ground adds to that from point D to ground so that vectors CG and DG are represented by arrows pointing upwards. However, if point G had been used as the reference point instead of point A, the vector GD would have been shown with the direction of the arrow reversed since the voltage from point C to ground is 180 degrees out of phase with that from point D to ground. The vector voltages at points C and D are then 90 degrees ahead ci the voltage AB at the cathodes of the tube V5 and the voltage to ground at point C is 180 degrees out of phase with the voltage to ground at point D. The voltages from UlA the points C and D are connected to any suitable push-pull amplier |20.

These voltages are amplified and inverted by the amplifier |20 and applied to the plates of a double diode tube V6 comprising the A. T. I. C. detector |2I, this double diode tube being similar to the tube V4 shown in Fig. 2. Like the arrangement including the tube VAI. in Fig. 2, a signal from the signal selector 25 is appliedto the two plates of the double diode tube VE. The signal from the signal selector 2G applied to the detector I2| is a positive pulse which raises the voltage of both plates of the double diode by an equall amount. Since the 410-kilocycle gating'waves have been shifted degrees in phase by the action of the tube V5 and its associated circuits to become the waves |5|iand |5| shown in Fig. 4-I, the right section of the double diode V6, for example, will be conducting during the middle 200 yards of the pulse Hi8 while the other half of this tube is cut off. Therefore, a video signai occurring within i yards of the center of the 40G-yard pulse |38 will cause an additional flow of current in one half of the tube V 3 but not in the other half. Fig. 4-J shows the current pulses |52 and |53 through the two halves of V6 due to the gating waves alone, Fig. 'fl-K shows the current wave |54 through one diode and Fig. 4-L shows the current wave through the other diode when the selected echo |09 is within the middle 200 yards of the 40G-yard pulse |93. However, if the signal occurs within lili) yards of either edge of the 40G-yard range pulse, an additional flow of current will occur in the other diode, that is, the second or third half sine wave in the wave |55 in Fig. 4,-L will be larger (depending on whether the selected echo |59 is near the left or right edge ofV the pulse |08) while the current in the rst half of the diode will remain unchanged.

The voltages in the cathode circuits of the tube VB are integrated by the condenser connected to them and produce positive signal voltages at the grid of the push-pull direct coupled amplifier |30. If no signal is present within the 40G-yard range interval spanned by the pulse |08, these voltages are equal and the amplied voltages applied to the tube V`| are equal. Tube V'I, which is the heart of the relay control arrangement of this invention, comprises a double triode, the control grids of which receive the output signals of the direct coupled arnplier it through resistors |3| and |32. The cathodes are connected together and through a resistor |33 to ground. The control grids are connected to ground through condensers |34 and |35 respectively. The left anode is connected to the positive terminal of the source 45 through resistor |33 while the right anode is connected to the positive terminal of this source through resistors |31 and |36, The coil of the A. T. I. C. relay 94 is connected across the resistor |31, the relay also having an armature |39 and a contact IAQ. Under this condition the plate current of the tube V'i is made insufficient to operate relay 94. If the signal is within plus i or minus 100 yards of the center of the pulse |08,

one grid of the tube Vl, say for example, the left grid, is driven in the negative direction. Since the cathodes of the tube V1 have a common resistor |33, this reduction of the current in the left cathode will reduce the bias and increase the plate current in the right section of the tube V'I', If the video signal from the signal selector 20 is of sufficient magnitude, this increase in plate current will cause the relay 94| to operate. A

75 signal occurring within 100 yards of either edge of the .pulsa lzshowrnin Fig. 4-Gzcausesfan in'- crease in the current through the lefthalf ofthe tube' :VT and Vazdecreaseiin the current through the :right r half. Undert this.: conditionA the plate currentthat flows'through the relay v94 isinsufii= cient to cause it to operate.

- 'An important advantage of: the cathode resistor I 33fcommon. t'o the two-cathodes ofthe'tube 4V1 is that'the'operation offtheztube V1 issmade dependent. substantially 'only uponthe .difference ofl potentiall between-'the two input (grid) leads and relatively: independent of the laverage upotentialof thesetw'o'leads.' `Signals Which-tendrto varythe potentials:V of both leadstogether (i.. e. socalled' .longitudinal: signals) are suppressed while signals-which tend to-vary' the potentials of the-two leads oppositely- (i: e. so-'called tr-ansversev signals) are amplified so-thatrelayglil is actuated byithisV latter type of signal. to'thesebstantial exclusion ofithe formeny As .the relay, 94 does not givea trueiaction if theselongitudinal signals are large, it is important to suppressthern. This suppression is obtained.LY in the present invention-even though a simple :two-terminal relay coil' isprovided in the output 'circuit' of -one onlyof the triodes making up :thetube V1.

It can` be shownthat'the' gridfvoltage: to plate Currentgainl of .the tube :VT to longitudinal'signals GL'HMM (l) wheregm. isk the4 transconductance of either'; of the triodes of AVl. and R is lthe resistance of the member |33. =(The expression neglectstheresistance-of the relay winding.) Theexpression for the. gain ofthe tube V-'I to transversesignals Y GT'=9'm The longitudinal suppression .ratio is'.therefore If a value of *gm of 2,000micro1-mhos and a value of R of 15,000 ohms are used', it is seen' that the longitudinal suppressionratio forthis set of assumed values is equal to 61.` In; other words, the gain of transverse signals is (il-times-that'of longitudinal signals.

'l' f The' operation ofthe rela'y- 94 causes the' operai tion'ofrelay 34.' Theoperationfof thefrelayfll causes-the `armature 1112V to makecontact with thecontact l 4-3"which 'closesthe vcircuit through th'e directcurrent source YV|44 tof cause-current to passthrought the automatic tracking- -ir'idicatorF S5 which ma'ysbgior example, adlevicewlfiichl` gives a visible oran audible indication? The operation of4 the relay'JI Sliifalscr causes the varrr'raturee 33=to -be moved from Vav position inL vcontact"withA the' contact element 32 to a position in contact1withcon` tact lmem'ber 3 i; or in other word'sl toactuate' the armatureis 33 from the' manualI to` the` automatic position.` 'The relation of lthe contact members? 3 i SZTandI- 33; tcthe motor' 281 and the amplierif83' i'sindicated 'schematically inzFig. 1. It is obviou'sithat theoperation ofthe AJ T. I; C. relaif'l canib'e usedf tot perform. Iother switching or4 conditioning operations than those lspecica'lly mentioned 'abovel For'example; if,` the :radar is one whichhas'lautomatic antenna tracking such a`s.that,l for lexample, disclosed inY the f copending application of 'l B'. M. Oliver; y Serial '.No.-11523,722, filed February 24, 1944,",andLwhich istnovv United States YPatent 2,451,632; :ther energizationA of `this relay maybe used toconnect for automatic tracking' motors driving-.the Vantennay through Ahorizontal andfvertical angles, while the deenergization of the relay Mmaybe utilized to condition the. circuit .for manual operation of these motors in a manner'similar tothe operation of the motor 28 bythe handwheelfcontrol 80.

Circuit' constants of a` radar arrangement in accordance with the invention which `has 'been actually' `constructed and satisfactorilyl operated have been indicated'on the drawings. It is to be understood, however, that the invention isnot limitedto the use of elements having ythese particular circuit constantsnnor is the invention limitedto use in radar systems. `In the drawings, the reference letter -w is` used in connectionvwith resistances in lieu ofthe word ohms while the reference letter Q is -used in the same connection to be representative of the word megohms Although the present invention has been described in terms of a preferred illustrative embodiment, it should be realized .that the invention andits several yfeatures are. susceptible of embodimentin awide .variety of other forms and hence the invention is to be understood as comprehending.. such otheriormsasmay fairly come within the spirit and letter. ofthe claim.

- What. iscla-med is:

A differential control system for utilizing differences between Ya iirst and a second input signal comprising arst and a second source of inputY signals capable of being continuously variable, a` first and a second space current deviceVeach having a plate, a cathode, and a control grid, a'rst meansV for connecting the rst of 'saidplates to ground through a path which comprises a source of direct potential, a second means for connecting the second of said pla-tes to ground through a path which comprises a load device and a source of direct potential, a third means for supplying a .first and a second continuously variable unidirectional signal to the control grids of. the first and second devices, respectively, and a fourth means, including a high resistanceconnected between the cathcdes ot said two devices and ground, responsive to the first vsignal tor varying the plate current of the second device, said third means and said fourth means cooperatingr to make the plate current in said second space current device substantially responsive only' to diierences between the rst and second signals. l

'BERNARD M. OLIVER.

ABEFERENCES J CITED The vfollowing references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,265,825 Urtel et al Dec. 9, 1941 2,274,158 Penther Feb. 24, 1942 2,369,081 Shook et al. Feb. 6, 1945 2,416,223 Sanders Feb. 18, 194'? OTHER REFERENCES VReview of .Scientific Instruments, August 1941,' page 412. 

